Architecture: We can love the man who loves concrete: As the architect of the National Theatre turns 80, Peter Dormer puts the case for his imaginative Modernism

Sir Denys Lasdun, one of Europe's most important post-war architects, is 80 this month. His ideas are bound to become ever more influential among architects but Lasdun, the creator of the Royal National Theatre, has a fascination with concrete, a material that many of us hate. Should we - can we - exercise a little 'mind over matter' and love Lasdun for his imagination?

His best-known buildings, apart from the National Theatre, include the Royal College of Physicians, London, the University of East Anglia, Norwich, and Christ's College, Cambridge. Such buildings are complex. They are not like the inflated sheds that many inferior architects working in both the Modern and Post- Modern styles have dumped upon us. His major works are monumental designs that combine practicality and symbolism; they are buildings intended to convey the values of the work that each particular building houses - be it a theatre or a university.

The architectural historian William Curtis has written a thoughtful study of Lasdun, published this month by Phaidon. Curtis tells us that before Lasdun enrolled as a student at the Architectural Association in 1932, he had a short but 'chaotic stint' at the Royal College of Music. Music, Curtis suggests, has contributed to a sense of rhythm, ratio and progression in Lasdun's architecture.

Other early Lasdun interests included the work of two radical architects, Le Corbusier and Nicholas Hawskmoor, Cubism and contemporary painting.

When he left the Architectural Association Lasdun worked in the office of Wells Coates, architect of the Isokon Flats, Lawn Road, London, which were an early example of English Modernism. Then he worked at Tecton, Berthold Lubetkin's architectural practice. Lubetkin was the leader of England's Modern movement.

During the war, as an officer in the Royal Engineers, Lasdun built airstrips and a fighter station in Holland. He became fascinated with the process of using bulldozers to sculpt land into platforms and mounds.

With hindsight these ingredients and more can be seen in the first of Lasdun's major buildings - the Royal College of Physicians of 1959, which stands beside a John Nash terrace in London's Regent's Park. This is perhaps the most popular of Lasdun's buildings - and the one in which exposed concrete is least evident. Curtis says it inspired his interest in Lasdun: 'Here was a building that reminded me of abstract painting yet stood comfortably next to Nash. Modern but with Classical overtones . . .'

Medicine is an imaginative discipline whose moral importance is rivalled only by that of law. Lasdun's design for the Royal College of Physicians mirrors this importance by being serious and grand but not pompous.

The long horizontal forms of the main building, faced with white glass mosaic, are played off against a steely-blue brick mound housing the lecture theatre. Inside, the main staircase appears to float, like an ethereal processional way. As Lasdun says, from the hall and the main stairs 'the whole anatomy of the building is made visually clear'. He has demonstrated that Modernism provides the appropriate architecture for contemporary civic and professional values. I cannot think of any 'Post-Modern' building in Britain that succeeds so well in responding to a major theme.

The anatomy of Lasdun's other popular building, the Royal National Theatre, is not so clear. Some people complain that they become disorientated when they make their way from level to level. Yet the interior of the National is well-used, thronged, not only with playgoers but also with people wanting a meal or a drink and some free entertainment from the musicians in the foyer.

Of the two main theatres at the National, that of the Olivier is especially magical; it evokes a sense of an otherworldly vastness - it is a gigantic visual metaphor for the imagination. And it is in concrete - but the concrete is softened by the rising semi-circular tiers of fabric-coated seating and the clever washes of light and shade created by the light playing on the textured walls.

The outside of the National is an example of Lasdun's concept of urban landscape. The building rises in terraces which look like rock strata. But although the building does fit in with the grain and texture of the city, it remains a bleak vision for those who only pass by; it is through use that the National becomes 'lovable', because the ideas of the building come alive for the senses as well as the mind.

Some of Lasdun's ideas for buildings would have been intolerable had they been built. It was an excellent thing for Cambridge that Lasdun's proposal for a cluster of three laboratory towers was turned down in 1961. The towers would have dramatically altered the famous view of King's College Chapel from the 'Backs'.

Curtis argues that the vertical planes of Lasdun's laboratory towers would have acted as a foil to the English Perpendicular style of King's Chapel, and that the basic forms of the towers echoed the shape of the Octagon of the cathedral in nearby Ely. But a building must speak for itself; it will not get by through hanging on to strained comparisons with other, more favoured buildings.

Lasdun's designs are not, of course, shaped only by his aesthetic tastes. He puts a huge emphasis upon research and has avoided architectural competitions because they do not provide the umbilical cord of information between the architect and the user. Yet the nature of this information is not always particularly scientific. In 1962, when he began designing the students' residences at the University of East Anglia, Lasdun was asked to consider the question: 'How should young people live in a new university?' He was apparently impressed by a radio broadcast in which a sociologist said that young people were independent, romantic puritans who saw life as arbitrary and malevolent. This choice piece of Sixties thinking, together with the site of 'water, marsh, slope, trees, meadows and parkland', inspired the design for a string of student residences that follow the contours of the land like a cliff and which at the same time step back in a series of terraces like a ziggurat.

The residences are chains of 'habitats', each consisting of 12 study bedrooms and a kitchen. Every room has a wonderful view, and in terms of their functional design and visual effect the buildings can be said to capture the informality, independence and romantic aspects of the 'brief'. However, the upper walkways and the science buildings behind the residences are massively concrete, and whether or not they encourage the students to feel that life is arbitrary, they certainly make me wonder about its malevolence.

Yet the views that Lasdun has created between the student residences, and those to be enjoyed from the concrete highwalk, are wonderful. They remind me that the elements of perfection that Lasdun has created in his architecture demand as much policing and protecting as that which we automatically give to the work of architects from earlier centuries.

(Photograph omitted)